Previously established synthetic methodology for the creation of quaternary carbon centers by operations involving the geminal disubstitution at a carbonyl carbon atom are being extended to allow the enantioselective construction of fully substituted carbons. Several of these procedures are also being applied to the syntheses of biologically-active natural products, especially alkaloids of the Amaryllidaceae family. Of particular interest, is the development of efficient total syntheses of pretazettine which is an anticancer/antiviral agent together with the related alkaloids precriwelline, tazettine, and galanthamine. Selected synthetic intermediates and analogs of pretazettine will be submitted to the National Cancer Institute for biological evaluation.